The present invention relates generally to a hybrid lens for collimating a divergent input wavefront with low optical aberrations and more particularly to a hybrid lens whereby a first surface of the lens diffracts the divergent wavefront and a second surface of the lens refracts the divergent wavefront so as to collimate the lens' output with low optical aberrations.
Many optical sources, such as diode lasers, produce asymmetrically diverging output beams. Diode lasers are currently utilized in many applications. Many of these applications require a collimated diode laser output with low optical aberrations even though diode lasers typically produce asymmetrically diverging output beams. In many instances, this asymmetric divergence may be quite fast, such as an 80.degree. output fan or larger, from the individual diode laser.
There have been a variety of proposed optical design solutions to collimate, with low optical aberrations, the asymmetrically diverging wavefronts. One proposed solution is to mold plastic or glass aspheric optical elements in the shape desired in order to collimate the diverging output beam. An example of such a molded glass optical element is discussed in "Precision Molded-Glass Optics," written by R. Maschmeyer, et al. in Applied Optics, vol. 22, No. 16, on page 2410 in 1983. The glass optic elements which have been molded are generally limited in their ability to collimate a divergent output beam, however, due to stresses inherent in the glass element from the molding process. Additionally, molded plastic optical elements, while easier to mold than the relatively difficult to mold glass elements, tend to deform when subjected to high temperatures. Such deformation limits the plastic elements ability to collimate diode laser's output since high temperatures would often be experienced when the optical element was placed adjacent to the emitting facet of the diode laser.
An alternative method collimating a divergent wavefront involves the use of gradient index (GRIN) lenses such as the lens described in U.S. Pat. No. 4,668,053 which issued to Hissmi Nishi, et al. on May 26, 1987. While such GRIN lenses may be capable of collimating a divergent wavefront, their manufacture is typically complex. This complexity is due to the traditional methods of producing a GRIN lens by either chemical leaching of a glass rod, such that the refractive index is varied along the radius of the rod, or chemical vapor deposition of layers of particles having varied refractive indices, such that there is a concentric variation in the rod's refractive index. Thus, due to the typically complex methods for fabricating a GRIN lens, the utilization of such lenses is somewhat limited since they are quite expensive and require a sophisticated manufacturing process.
Another approach for producing an optical element for collimating a divergent output is illustrated in U.S. Pat. No. 4,895,790 (hereinafter the '790 patent) which issued to Gary J. Swanson, et al. on Jan. 23, 1990 which proposes the manufacture of diffraction-based, computer-generated binary optical elements. While such a method of manufacturing is discussed in the '790 patent, the actual process for determining the profile of a binary optical element is not discussed so as to enable one skilled in the art to construct a binary optical lens element to collimate a divergent input.
Therefore it would be desirable to provide an optical element which is capable of collimating, with low optical aberrations, a highly divergent wavefront. Furthermore, it would be desirable if such collimating optical elements were efficient such that a substantial percentage of the divergent input wavefront was retained in the collimated output.